1. Field of the Invention
The present invention relates to a method for manufacturing a master disk used for manufacturing an optical disk which is an optical recording/reproducing medium, and to the master disk.
2. Description of Related Art
In general, a high density optical disk such as a digital versatile disk (DVD)--random access memory (RAM) includes grooves 1 and lands 2 where information are recorded along spiral tracks, as shown in FIG. 1. Also, pits 3 are formed on the grooves 1 and the lands 2, respectively, to thereby record desired information thereon. Since both the grooves 1 and the lands 2 are used for recording information thereon, more information can be recorded as compared to a conventional disk in which either the groove 1 or the land 2 has been used for recording.
The optical disk is manufactured through processes as shown in FIGS. 2A through 2D. As shown in FIG. 2A, a photoresist 20 is coated on a substrate 10, and then the photoresist 20 is simultaneously exposed to a laser 30 for a groove and a laser 30' for a pit according to patterns of the groove 1, the land 2 and the pit 3 while rotating the substrate 10. Reference numerals 31 and 31 ' indicate modulators for turning on/off the lasers 30 and 30', respectively.
Subsequently, as shown in FIG. 2B, an etching reagent is sprayed on the exposed substrate 10, to thereby manufacture a master disk 15 where grooves, lands and pits are formed.
A son disk 25 is formed by stamping the master disk 15 as shown in FIG. 2C, and then an optical disk is copied by an injection molding method in which resin 35 is injected into a mold 40 having the son disk 25 mounted thereon, as shown in FIG. 2D.
However, in the above method, the lands, the grooves and the pits are formed on one photoresist layer by simultaneously exposing and etching the same, so that boundaries among the land, the groove and the pit are not sharp.
Accordingly, start and end points of information signals are not accurately detected during reproduction, which may cause jitter errors in which an output signal is not appropriately generated on time.